1. Field of the Invention
The present invention relates to a liquid ejection head that ejects liquid.
2. Description of the Related Art
A liquid ejection head for ejecting ink is generally mounted onto an ink jet recording apparatus for recording an image on a recording medium by ejecting the ink. As a mechanism for causing the liquid ejection head to eject ink, there is known a mechanism using a pressure chamber that is shrinkable in volume by a piezoelectric element. In this mechanism, the pressure chamber shrinks due to the deformation of the piezoelectric element to which a voltage is applied, and thus the ink inside the pressure chamber is ejected from an ejection orifice formed at one end of the pressure chamber. As one liquid ejection head including such a mechanism, there is known a so-called shear mode liquid ejection head in which one or two inner walls of the pressure chamber are constituted of a piezoelectric element. In the shear mode liquid ejection head, the pressure chamber is shrunk by shear deformation, instead of extension deformation and shrinkage deformation by voltage application to a piezoelectric element.
Regarding ink jet recording apparatus for industrial applications, there is a demand for use of high viscosity liquid. In order to eject high viscosity liquid, a large ejection force is required for the liquid ejection head. To satisfy this demand, there has been proposed a liquid ejection head called a Gould type, in which the pressure chamber is formed from a tubular piezoelectric member having a circular or rectangular sectional shape. In the Gould type liquid ejection head, the piezoelectric member is deformed by extension and shrinkage in the inward and outward directions (radial direction) about the center of the pressure chamber. In this manner, the pressure chamber expands or shrinks. In the Gould type liquid ejection head, the entire wall surface of the pressure chamber deforms, and this deformation contributes to the ink ejection force. Therefore, as compared to the shear mode liquid ejection head in which one or two wall surfaces are formed from the piezoelectric element, a larger liquid ejection force can be obtained.
In order to obtain a higher resolution, multiple ejection orifices in the Gould type liquid ejection head need to be arranged at a higher density. This requires that pressure chambers corresponding to the respective ejection orifices be arranged highly densely as well. Japanese Patent Application Laid-Open No. 2007-168319 discloses a method of manufacturing a Gould type liquid ejection head in which pressure chambers can be formed at a high density.
The first step of the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319 is to form multiple grooves extending in the same direction as one another in each of multiple piezoelectric plates. The multiple piezoelectric plates are then stacked on top of one another with the direction of the grooves aligned, and are cut in a direction orthogonal to the groove direction. The groove portions of each piece of cut piezoelectric plates constitute the inner walls of pressure chambers. Thereafter, piezoelectric members present between the pressure chambers to separate one pressure chamber from another are removed down to a given depth. A supply path plate plus an ink pool plate and a printed wiring board plus a nozzle plate are connected above and below, respectively, the piezoelectric plate where the pressure chambers have been completed. The liquid ejection head is thus completed. According to this manufacturing method, pressure chambers can be arranged in a matrix pattern and can therefore be arranged at a high density. In addition, with this manufacturing method, pressure chambers can be formed with high precision because the workability of forming grooves in a piezoelectric plate is better than that of boring holes in a piezoelectric plate.
In the liquid ejection head manufactured by the manufacturing method of Japanese Patent Application Laid-Open No. 2007-168319, multiple pressure chambers are arranged so that a space is provided between pressure chambers. In other words, wall portions constituting each pressure chamber are constructed independently. Therefore, increasing the length (height) of pressure chambers in order to eject a highly viscous liquid (i.e., to increase liquid ejection force), in particular, reduces the rigidity of the liquid ejection head. A pressure chamber low in rigidity is susceptible to folding and may consequently be incapable of ejecting liquid.
Another problem with a liquid ejection head in which multiple piezoelectric plates are stacked is misalignment between layers due to an error when positioning the piezoelectric plates, which causes each pressure chamber to deform by a different amount and can fluctuate ejection performance from one ejection orifice to another.